U.S. patent number 6,441,715 [Application Number 09/505,051] was granted by the patent office on 2002-08-27 for method of fabricating a miniaturized integrated circuit inductor and transformer fabrication.
This patent grant is currently assigned to Texas Instruments Incorporated. Invention is credited to F. Scott Johnson.
United States Patent |
6,441,715 |
Johnson |
August 27, 2002 |
Method of fabricating a miniaturized integrated circuit inductor
and transformer fabrication
Abstract
A method for fabricating inductors and transformers on
integrated circuits. A magnetic material is formed on the
semiconductor substrate. The magnetic material comprises a
suspension of magnetic material in an insulator. A metal film is
formed that forms at least one coil around the magnetic material
forming an inductor structure. Two adjacent coils can be linked
with the magnetic material to form a transformer.
Inventors: |
Johnson; F. Scott (Garland,
TX) |
Assignee: |
Texas Instruments Incorporated
(Dallas, TX)
|
Family
ID: |
26818319 |
Appl.
No.: |
09/505,051 |
Filed: |
February 16, 2000 |
Current U.S.
Class: |
336/200;
257/E21.022; 257/E27.046; 29/602.1; 29/606; 336/223 |
Current CPC
Class: |
H01F
17/0006 (20130101); H01F 41/046 (20130101); H01L
27/08 (20130101); H01L 28/10 (20130101); H01F
17/0013 (20130101); H01F 17/0033 (20130101); Y10T
29/49073 (20150115); Y10T 29/4902 (20150115) |
Current International
Class: |
H01F
17/00 (20060101); H01F 41/04 (20060101); H01L
21/02 (20060101); H01L 27/08 (20060101); H01F
005/00 () |
Field of
Search: |
;29/602.1,605,607
;336/200,223,232 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Mai; Anh
Attorney, Agent or Firm: McLarty; Peter K. Brady, III; W.
James Telecky, Jr.; Frederick J.
Parent Case Text
This application claims priority under 35 USC .sctn.119(e)(1) of
provisional U.S. application Ser. No. 60/120,374 filed Feb. 17,
1999.
Claims
I claim:
1. A method of forming an inductor in a semiconductor substrate
with an upper surface, said method comprising the steps of: forming
a magnetic film on said upper surface of said semiconductor
substrate; patterning said magnetic film using photolithography;
forming a metal film on said upper surface of said semiconductor
substrate; and patterning said metal film such that said metal film
forms at least one coil around said magnetic film.
2. The method of claim 1, wherein said magnetic film comprises a
material selected from the group consisting of: Ni, Ni--Cu--Cr,
Mn--Zn-Ferrite, and any combination thereof.
3. The method of claim 1 wherein said magnetic film comprises a
stack of alternating layers of a magnetic film and an insulating
film.
4. The method of claim 1 wherein said magnetic film comprises a
suspension of a magnetic material in an insulating material.
5. A method of forming an inductor in a semiconductor substrate
with an upper surface, said method comprising the steps of: forming
a first magnetic film on said upper surface of said semiconductor
substrate wherein said first magnetic film has a upper surface;
forming a first insulating layer on said upper surface of said
first magnetic film wherein said first insulating layer has an
upper surface; forming a second magnetic film on said upper surface
of said first insulating layer; patterning said second magnetic
film using photolithography; forming a metal film on the upper
surface of said first insulating layer; patterning said metal film
such that said metal film forms at least one coil around said
second magnetic film; forming a second insulating layer with an
upper surface on said upper surface of said first insulating layer
wherein said second insulating layer completely encases said second
magnetic film and said metal film; and forming a third magnetic
film on said upper surface of said second insulating layer.
6. The method of claim 5, wherein said first magnetic film
comprises a material selected from the group consisting of: Ni,
Ni--Cu--Cr, Mn--Zn-Ferrite, and any combination thereof.
7. The method of claim 5, wherein said second magnetic film
comprises a material selected from the group consisting of: Ni,
Ni--Cu--Cr, Mn--Zn-Ferrite, and any combination thereof.
8. The method of claim 5, wherein said third magnetic film
comprises a material selected from the group consisting of: Ni,
Ni--Cu--Cr, Mn--Zn-Ferrite, and any combination thereof.
9. The method of claim 5 wherein said first magnetic film comprises
a stack of alternating layers of a magnetic film and an insulating
film.
10. The method of claim 5 wherein said second magnetic film
comprises a stack of alternating layers of a magnetic film and an
insulating film.
11. The method of claim 5 wherein said third magnetic film
comprises a stack of alternating layers of a magnetic film and an
insulating film.
12. The method of claim 5 wherein said first magnetic film
comprises a suspension of magnetic material in an insulating
material.
13. The method of claim 5 wherein said second magnetic film
comprises a suspension of magnetic material in an insulating
material.
14. The method of claim 5 wherein said third magnetic film
comprises a suspension of magnetic material in an insulating
material.
Description
FIELD OF THE INVENTION
The invention is generally related to the field of semiconductor
device fabrication and more specifically to a method for
fabricating inductors and transformers on integrated circuits
BACKGROUND OF THE INVENTION
As more circuit components are being integrated on-chip there is an
increasing need for integrated circuit inductors. Inductors in
integrated circuits have a number of important uses in providing
on-chip filtering and voltage conversion. Currently, the majority
of inductors used are discrete off-chip devices that require
connection to the integrated circuit (IC). The leads used for the
connection adds series resistance and capacitance to the overall
circuit and therefore affect the performance of the circuit. In
addition, there is an additional cost associated with these
discrete external inductors.
With the current trends towards system-on-a-chip integrated
circuits, it is often the case that a number of different supply
voltages are required on the integrated circuit. Typically, a
single voltage is supplied to the IC and the remaining required
voltages are obtained through voltage conversion. On-chip voltage
conversion usually requires an IC transformer and filtering. This
filtering is performed using capacitors and inductors. IC
transformer fabrication requires efficient coupling of inductive
coils and relatively large values of inductance.
Currently, IC inductors are typically fabricated as a coil in a
single level of metal or using a system of multiple metal levels
along with vias connecting the metal levels. Here, the core of the
inductor will be the interlevel dielectric material which in most
cases will be silicon dioxide. The fabrication of integrated
circuit inductors with large inductance values having SiO.sub.2 as
the core is made difficult due to the low relative permeability of
SiO.sub.2 and the presence of traps and other defects in the
SiO.sub.2 layer. If a large number of turns are used to increase
the inductance, the silicon surface area required becomes
prohibitively large.
Using current fabrication methods, large value inductors take up a
large amount of silicon surface area making their use in current IC
technology impractical.
SUMMARY OF THE INVENTION
The instant invention describes a method for fabricating a
miniaturized integrated circuit inductor and transformer.
An embodiment of the instant invention is a method of forming an
inductor in a semiconductor substrate with an upper surface, said
method comprising the steps of: forming a magnetic structure on
said semiconductor substrate; and forming a metal structure on said
upper surface of said semiconductor substrate such that a magnetic
flux is induced in said magnetic film. Another embodiment of the
instant invention is a method of forming an inductor in a
semiconductor substrate with a upper surface, said method
comprising the steps of: forming a first magnetic structure on said
semiconductor substrate; forming a first insulating layer on said
first magnetic film; forming a second magnetic structure on said
first insulating layer; forming a metal structure on said second
first insulating layer such that said metal film induces a magnetic
flux in said second magnetic film; forming a second insulating
layer with an upper surface on said first insulating layer wherein
said second insulating layer encases said second magnetic film and
said metal film; and forming a third magnetic film on said second
insulating layer.
Another embodiment of the instant invention is an integrated
circuit transformer in a semiconductor substrate comprising: a
first metal film with a first pattern; a continuous magnetic layer
above said first metal film; a second metal film above said
magnetic film with a second pattern; a plurality of electrically
conducting contacts between said first metal film and said second
metal film wherein said first metal film, said second metal film,
and said electrically conducting contacts form two adjacent coils
with each coil having at least one turn around said magnetic
film.
BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings:
FIGS. 1a-1c are cross-sectional diagrams illustrating one
embodiment of the instant invention.
FIG. 2 is a top view of an embodiment of the instant
FIGS. 3a-3c are cross-sectional diagrams illustrating an embodiment
of the instant invention.
FIG. 4 is a top view of an embodiment of the instant invention.
FIG. 5 is a top view of a transformer formed using an embodiment of
the instant invention.
FIG. 6 is a top view of a toroidal like inductor formed using an
embodiment of the instant invention
DETAILED DESCRIPTION OF THE INVENTION
The invention will now be described with reference to FIGS. 1-5. It
will be apparent to those of ordinary skill in the art that the
benefits of the invention can be applied to other inductor and
transformer structures. In this disclosure, the term "magnetic"
refers to a material with paramagnetic, ferromagnetic, or
ferrimagnetic properties which can be used to modify the magnetic
field and therefore the inductance of the coil. It also refers to a
diamagnetic material (eg. silver or lead) which may be used to
reduce the magnetic field in all or a given portion of a coil or
the area around a coil.
For an embodiment of the instant invention, a semiconductor
substrate 10 with a dielectric layer 80 is shown in FIG. 1a. The
substrate 10 is preferably comprised of single-crystal silicon or
an epitaxial silicon layer formed on a single-crystal silicon body
and may have existing circuits fabricated in other areas which are
not shown for clarity. The dielectric layer 80 preferably comprises
an oxide, a nitride, or any combination thereof. As shown in FIG.
1, a first magnetic layer 20 is formed on the surface of the
dielectric material 80. In one embodiment this first magnetic layer
comprises a Ni, Ni--Cu--Cr, or Mn--Zn-Ferrite film. However
magnetic layer 20 may be comprised of any magnetic film compatible
with semiconductor processing technology. In another embodiment,
the first magnetic layer 20 comprises a stack of alternating layers
of magnetic material and an insulating material. The magnetic
material in the stack is preferably comprised of Ni, Ni--Cu--Cr,
Mn--Zn-Ferrite film or any magnetic film compatible with
semiconductor processing technology. The insulating material in the
stack preferably comprises silicon oxide, silicon nitride,
photoresist, polymers, any combination thereof, or any insulator
compatible with semiconductor processing. In another embodiment,
the first magnetic layer 20, comprises a suspension of magnetic
material in an insulator. The suspended magnetic material
preferably comprises Ni, Ni--Cu--Cr, Mn--Zn-Ferrite, or any
magnetic material. The insulator material containing the suspension
of magnetic material preferably comprises a polymer, polyamide,
silicon oxide, photoresist, BPSG, PSG, HSQ, spin-on-glass, aerogel
or xerogel. The insulator material should comprise a material that
is easily flowed unto the substrate and to which the suspension of
magnetic material is easily added. A first insulator layer 30 is
formed on the surface of the first magnetic layer 20. In one
embodiment, the first insulator layer 30 comprises oxide, polymer,
polyamide, photoresist, BPSG, PSG, HSQ, spin-on-glass, aerogel,
xerogel, a nitride, or any combination thereof. A second magnetic
layer 40 is formed on the surface of the first insulator layer 30,
and patterned using standard photolithographic techniques. The
second magnetic layer 40 may be comprised of the same material as
the first magnetic layer 20. As illustrated in FIG. 1b, a metal
film is formed on the surface of the first insulator layer 30, and
patterned to form a coil 50. In an embodiment of the instant
invention, the metal film 50 comprises Al, Cu, Ti, W, Mo, Co, Pt,
Pd, or any combination thereof. FIG. 2 illustrates an embodiment of
the coil 50. Such a coil 50 should comprise at least one turn and
is not limited to any particular shape.
Referring to FIG. 1c, a second insulator layer 60 is formed
encasing the coil 50 and the second magnetic material 40. Second
insulator layer 60 may be comprised of oxide, polymer, polyamide,
photoresist, BPSG, PSG, HSQ, spin-on-glass, aerogel, xerogel, a
nitride, or any combination thereof. A third magnetic layer 70 is
formed on the surface of the second insulator layer 60. The stack
formed by the third magnetic layer 70 and second insulator layer 60
is patterned using standard photolithographic techniques resulting
in the structure illustrated in FIG. 1c. A top down view of the
completed structure is shown in FIG. 2.
An advantage of the embodiment of the instant invention shown in
FIG. 1c and FIG. 2 is that large value inductors can be fabricated
over a semiconductor wafer and integrated with other devices. In
addition, the magnetic layers 20 and 70 will contain the magnetic
field to within a small distance beyond these layers thereby
reducing the interaction between the magnetic field produced by the
coil 50 and any nearby circuits or circuit elements.
In an alternative embodiment of the instant invention, a
semiconductor wafer 100 is shown in FIG. 3a. The wafer 100 may have
existing circuits fabricated in other areas which are not shown for
clarity. A first insulator layer 800 is formed over the substrate
and comprises an oxide, polymer, polyamide, photoresist, BPSG, PSG,
HSQ, spin-on-glass, aerogel, xerogel, a nitride, or a stack of any
of the above. A first metal film 200 is formed on the surface of
the first insulator layer 800 and patterned using known
photolithographic techniques. In one embodiment the first metal
film 200 comprises Al, Cu, W, Mo, Co, Pt, Pd, or any combination or
stack thereof. A second insulator layer 300 is formed encasing the
first metal film 200. Second insulator layer 300 preferably
comprises an oxide, polymer, polyamide, photoresist, BPSG, PSG,
HSQ, spin-on-glass, aerogel, xerogel, a nitride, or any combination
thereof. As shown in FIG. 3b, a magnetic layer 400 is formed on the
surface of the second insulator layer 300. In one embodiment, the
magnetic layer 400 comprises a Ni, Ni--Cu--Cr, Mn--Zn-Ferrite film
or any combination thereof or any magnetic film compatible with
semiconductor processing technology. In another embodiment, the
magnetic layer 400 comprises a stack of alternating layers of
magnetic material and insulator material. The magnetic material in
the stack may comprise Ni, Ni--Cu--Cr, Mn--Zn-Ferrite film or any
magnetic film compatible with semiconductor processing technology,
and the insulator material in stack comprises silicon oxide,
silicon nitride, photoresist, polymers, or any insulator compatible
with semiconductor processing. In another embodiment, the magnetic
layer 400, comprises a suspension of magnetic material in an
insulator. The suspension of magnetic material comprises Ni,
Ni--Cu--Cr, Mn--Zn-Ferrite, or any magnetic material. The insulator
material containing the suspension of magnetic material comprises
an oxide, polymer, polyamide, photoresist, BPSG, PSG, HSQ,
spin-on-glass, aerogel, xerogel, a nitride, and any combination
thereof. The insulator material should comprise a material that is
easily flowed onto the substrate and to which the suspension of
magnetic material is easily added. The magnetic layer 400 is
patterned using known photolithographic techniques. A third
insulator layer 500 is formed encasing the magnetic layer 400. The
third insulator layer comprises an oxide, polymer, polyamide,
photoresist, BPSG, PSG, HSQ, spin-on-glass, aerogel, xerogel, a
nitride, or any combination thereof. A number of openings or vias
600 are formed in the third insulator layer 500 that expose the
surface of the underlying first metal film 200. A second metal 900
is formed that contacts the underlying first metal film 200 and
completely fills the openings or vias 600. In one embodiment this
metal comprises W, Al, Cu, Ti, TiN, or a stack thereof and is
formed using known semiconductor processing technology. As shown in
FIG. 3c, a third metal film 700 is formed on the surface of the
third dielectric layer 500. The third metal film 700 is preferably
comprised of Al, Cu, W, Mo, Co, Pt, Pd, or any combination or stack
thereof and is patterned using known photolithographic techniques
resulting in the structure shown in FIG. 3c. A top down of the
completed structure is shown in FIG. 4.
The structure illustrated in FIG. 3c and FIG. 4 form an inductor
with a magnetic core. Shown in FIG. 5 is an embodiment of a
transformer. The magnetic material 400 is extended to encompass two
adjacent inductors 1000 and 2000. The structure is formed using the
method described above and shown in FIGS. 3a-3c. In another
embodiment of a transformer, the magnetic layer 400 in FIG. 5 is
patterned to form a circle and the various layers 200, 700, and 600
will follow the shape of the circle. To form a toroid transformer,
the layers 200, 700, and 600 will form two coils, each coil
circling a semicircle of layer 400.
FIG. 6 illustrates another embodiment of the instant invention
showing the formation of a toroid like inductor. In FIG. 6, the
magnetic layer 400 could also be patterned in the form of a circle
and the layers 200, 600, and 700 following the shape of the circle.
In fact, any shape of the magnetic layer 400 could be used.
An advantage of the embodiment of the instant invention shown in
FIG. 3c and FIG. 4 is that large value inductors can be fabricated.
In addition, the embodiment facilities the fabrication of a new
class of integrated circuit transformers as shown in FIG. 5.
While this invention has been described with reference to
illustrative embodiments, this description is not intended to be
construed in a limiting sense. Various modifications and
combinations of the illustrative embodiments, as well as other
embodiments of the invention will be apparent to persons skilled in
the art upon reference to the description. It is therefore intended
that the appended claims encompass any such modifications or
embodiments.
* * * * *